# Magnetic fields

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#1
A beam of electrons is fired between a pair of parallel plates which are 2.0 cm apart. The potential difference between these plates is 4.0 kV. The electron beam is running in a direction parallel to the plates and perpendicular to a magnetic field of 0.15 T. In order for the electrons to not be deviated, they must be travelling at:
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4 weeks ago
#2
(Original post by Mlopez14)
A beam of electrons is fired between a pair of parallel plates which are 2.0 cm apart. The potential difference between these plates is 4.0 kV. The electron beam is running in a direction parallel to the plates and perpendicular to a magnetic field of 0.15 T. In order for the electrons to not be deviated, they must be travelling at:
For the beam not to deviate, the forces due to the two fields must be equal and opposite.
You should know the formula for the force, F, on an electron due to the electric field, E. The strength, E, of that field is found from the pd and plate separation given in the question.

The formula for the force due to the magnetic field is
F=Bev
which depends on the speed, v, of the electrons. You are given the value of B in the question.

The 2 formulas together will allow you to calculate what value of v this needs to be.
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